Field of the Invention
The present invention relates to an image forming apparatus and an image forming system.
Description of the Related Art
Typically, an image forming apparatus using an electrophotographic process technique (for example, printer, copying machine, or facsimile) irradiates (exposes) a charged photoreceptor with a laser beam based on image data so as to form an electrostatic latent image. A developing apparatus supplies toner to a photoreceptor drum including the electrostatic latent image formed thereon. Therefore, the electrostatic latent image is visualized and then a toner image is formed. Furthermore, after the toner image is directly or indirectly transferred to paper by a transfer nip, the toner image is heated and pressurized by a fixing nip formed of a pressure roller and a heating roller so as to be fixed. As a result, an image is formed on the paper. Generally, the image forming apparatus can also form an image on continuous paper, such as continuous-form rolled paper or fanfold paper (hereinafter, referred to as continuous paper), or a recording medium including tacky paper (sticky paper) with glue adhering between a print side and release paper, continuing with no space between the pieces of paper. Hereinafter, the recording medium, such as paper or tacky paper (sticky paper) continuing with no space between the pieces of paper, is referred to as a continuous recording medium.
In a case where the image forming apparatus forms an image on the continuous paper, the continuous paper is present without being interrupted over the entire apparatus. Thus, the continuous paper is still present at a position of the fixing nip with printing stopping. The continuous paper is heated at the fixing nip. Thus, when remaining present at the fixing nip, the continuous paper present at the fixing nip is heated at the position of the fixing nip so as to receive damage, such as deformation or degeneration. Therefore, the image forming apparatus is required to convey the continuous paper in a small amount in a paper conveying direction, for example, at a conveying speed of approximately 10 mm/sec during a period during which the temperature of a fixing device decreases to a degree of temperature at which the continuous paper is not damaged, during a stop of a print job.
The image forming apparatus is required to convey the continuous paper in a small amount in the paper conveying direction during a period during which the temperature of the fixing device increases to temperature suitable for fixing in order to start the print job. In this manner, the image forming apparatus conveys the continuous paper in the small amount in the paper conveying direction so as to prevent the continuous paper from being damaged due to the heating at the fixing nip.
The continuous paper conveyed in the small amount in the paper conveying direction is delivered with no image formed. Thus, the continuous paper becomes wasted paper (hereinafter, referred to as waste paper). In order to inhibit occurrence of the waste paper, for example, the following configuration is thought. The image forming apparatus conveys the continuous paper in a direction opposite to the paper conveying direction, to the upper stream side of the transfer nip in the paper conveying direction before the next print job starts. Then, in the next print job, the image is formed on the continuous paper conveyed in the opposite direction. With this configuration, in the next print job, the image is formed on the continuous paper conveyed in the opposite direction after the continuous paper is conveyed in the small amount in the paper conveying direction. Thus, the continuous paper conveyed in the small amount in the paper conveying direction can be reused.
JP 3570335 B2 discloses an image forming system that forms an image on continuous paper. In the image forming system described in JP 3570335 B2, a buffer is provided between an image forming apparatus and a post-processing apparatus disposed at a subsequent stage of the image forming apparatus. Specifically, after operation of the post-processing apparatus stops, the continuous paper is conveyed from a transferring portion to a fixing portion so that slack of the continuous paper is formed at the buffer. Before the next print job starts, the slack portion of the continuous paper formed at the buffer is conveyed in a direction opposite to a paper conveying direction, to the upper stream side of a transfer nip in the paper conveying direction. With this configuration, a defect of an image in the slack portion and a jam that are caused by continuously forming the slack of the continuous paper during execution of the print job can be inhibited. The continuous paper to which post-processing has been performed, can be prevented from being conveyed in the opposite direction.
However, when the continuous paper that has passed through the fixing nip, is conveyed to the upper stream side of the transfer nip in the paper conveying direction, heat of the continuous paper heated at the position of the fixing nip is transmitted to a transfer roller and a transfer belt included in the transfer nip so as to cause damage, such as deformation and degeneration. Thus, a problem that a toner image cannot be transferred to a desired position at the transfer nip occurs. The continuous paper is heated at the position of the fixing nip so as to be deformed. Thus, in a case where the toner image is transferred to the continuous paper deformed at the transfer nip, a problem that unevenness occurs in the toner image, occurs. In a case where the image is formed with respect to the continuous recording medium, such as tacky paper (sticky paper) with glue adhering between a print side and release paper, instead of the continuous paper, the glue extruded upon pressurization of the fixing nip adheres to the transfer belt. Thus, a problem that the glue that has adhered to the transfer belt adheres to a surface of the continuous recording medium occurs. Furthermore, a mechanism for conveying the continuous paper in the direction opposite to the paper conveying direction, to the upper stream side of the transfer nip in the paper conveying direction, is required to be provided to the transferring portion of the image forming apparatus. Thus, a problem that the image forming apparatus becomes complicated occurs.